In a vehicle including an automatic transmission, when a driver suddenly depresses an accelerator pedal, downshift (kick-down) of the automatic transmission to a lower-speed side shift stage is automatically performed, and the vehicle thereby can obtain higher acceleration performance. Japanese Patent Application Laid-open No. 2006-176001 has made publicly known a pedal reaction force control device which includes a click mechanism for giving a click feeling by sharply increasing pedal reaction force at a predetermined stroke position where the accelerator pedal is depressed, and sharply decreasing the pedal reaction force when the accelerator pedal is depressed beyond the position, for the purpose of making the driver feel whether or not the accelerator pedal is depressed to a position where the kick-down is started.
In the conventional practice, the pedal reaction force control device including such a click mechanism is configured such that: as shown in Part (A) of FIG. 5, a stroke sensor converts a pedal stroke of the accelerator pedal into a voltage; when the voltage exceeds a predetermined voltage, it is judged that the accelerator pedal is depressed beyond the click position; and the kick-down of the automatic transmission is performed. However, in a case where as shown in Part (B) of FIG. 5, variation in mechanical precision of the click mechanism makes the click position of the accelerator petal different from one vehicle to another, and makes output voltage from the stroke sensor vary when the accelerator pedal is depressed beyond the click position, there is likelihood that: even though the accelerator pedal is depressed beyond the click position, the kick-down is not performed immediately; or before the accelerator pedal is depressed beyond the click position, the kick-down is carried out.
For example, even if the accelerator pedal is designed to be depressed beyond the click position when reaching a 70% stroke position, there is a case where variation in the click mechanism allows the accelerator pedal to be depressed beyond the click position when the accelerator pedal reaches a 80% stroke position. In this case, the output voltage from the stroke sensor reaches the predetermined voltage when the accelerator pedal reaches the 70% stroke position which is prior to the position where the accelerator pedal is depressed beyond the click position. As a result, there is likelihood that the kick-down which the driver does not expect is carried out.
On the other hand, in a case where the variation in the click mechanism allows the accelerator pedal to be depressed beyond the click position when the accelerator pedal reaches a 60% stroke position, there is a time lag between depression of the accelerator pedal beyond the click position at the 60% stroke position and arrival of the output voltage of the stroke sensor to the predetermined voltage at the 70% stroke position. As a result, there is likelihood that the kick-down is carried out later than the driver expects.
Particularly, if the kick-down is carried out before the accelerator pedal is depressed beyond the click position, the driver is given a significantly abnormal feeling. For this reason, the kick-down is prevented from being carried out before the accelerator pedal is depressed beyond the click position by setting a kick-down stroke, which is conventionally set as shown in a shift map in Part (A) of FIG. 6, to be lower as shown in a shift map in Part (B) of FIG. 6 with a possible error in the click position (a resultant possible error in the output from the stroke sensor) taken into consideration.
However, lower setting of the kick-down stroke makes vertical widths of shift lines in the shift map shown in Part (B) of FIG. 6 become narrower so as to make it difficult to sufficiently secure hysteresis for an upshift and a downshift. As a result, there is likelihood that drivability deteriorates.
Even if the click position of the click mechanism is accurate, such problems similarly occur in a case where there is variation in the output from the stroke sensor for converting the stroke of the accelerator pedal into the voltage. For this reason, control needs to be done to ensure that, by compensating for the variation in the precision of the click mechanism, the kick-down is carried out at a moment when the accelerator pedal is depressed beyond the click position.